1. Field of the Invention
The present invention relates to a cooling structure for a rotation object. More particularly, the invention relates to a cooling structure which is structured in the rotation object and cools the rotation object from inside.
2. Description of the Related Art
JP-A 2000-295818 discloses a cooling structure for a rotor of a motor. The rotor has a solid shaft, a pipe surrounding the shaft, and a rotor core fixed onto the pipe. A clearance is created between a surface of the shaft and an inner surface of the pipe, and acts as a cooling passage. That is, the rotor core is cooled by coolant flowing through the clearance.
An inlet passage and an outlet passage exist in the inside of the solid shaft, and are formed along an axis of the shaft. The inlet passage is connected to the cooling passage by a connection passage, and the outlet passage is connected to the cooling passage by another connection passage. The two connection passages are formed along the radius of the shaft.
In this structure, the coolant has to pass through four bends. That is, an angle between the inlet passage and the connection passage, an angle between the two connection passages and the cooling passage, and an angle between the connection passage and the outlet passage are all 90 degrees. Therefore, resistance to a stream of the coolant is large. Further, the resistance is increased with increase of a rotation speed of the rotor.
The present invention provides a solution to the above-mentioned resistance to coolant stream. The cooling method and structure provided by the present invention reduces the resistance without reducing performance of cooling.
According to a first aspect of the present invention, there is provided a cooling method for a rotation object. The rotation object has a rotation axis and an inner space. The inner space has a coolant inlet which is located on the rotation axis and a coolant outlet which is located on the rotation axis. The coolant inlet and the coolant outlet face each other. The cooling method comprises generating a main-stream of the coolant in a central space of the inner space, the main-stream flowing straightly along the rotation axis from the coolant inlet to the coolant outlet; generating a sub-stream of the coolant in a peripheral space around the central space, the sub-stream circulating in a radial direction of the inner space; and generating a contact between the main-stream and the sub-stream, the contact being attended with a mix of the coolant of the main-stream and the coolant of the sub-stream.
According to a second aspect of the present invention, there is provided a cooling structure for a rotation object. The rotation object has a center portion and two end portions. The center portion and the two end portions are arranged on a rotation axis of the rotation object. The two end portions are supported by bearings. The cooling structure comprises an inner surface enclosing an inner space which is inside of the center portion and is filled with coolant; an inlet passage being located inside of the one end portion and having a coolant inlet which is opened on the inner surface; and an outlet passage being located inside of the another end portion and having a coolant outlet which is opened on the inner surface; wherein the coolant inlet and the coolant outlet are located on the rotation axis and facing each other, so that a central space which is defined as a space between the coolant inlet and the coolant outlet and a peripheral space which is defined as a space around the central space are formed in the inner space.